U.S. patent application number 13/667622 was filed with the patent office on 2013-05-09 for lithium-ion battery with life extension additive.
This patent application is currently assigned to ROBERT BOSCH GMBH. The applicant listed for this patent is ROBERT BOSCH GMBH. Invention is credited to Jasim Ahmed, Paul Albertus, Nalin Chaturvedi, John F. Christensen, Aleksandar Kojic, Boris Kozinsky, Timm Lohmann, Roel S. Sanchez-Carrera.
Application Number | 20130115485 13/667622 |
Document ID | / |
Family ID | 47221579 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130115485 |
Kind Code |
A1 |
Christensen; John F. ; et
al. |
May 9, 2013 |
Lithium-Ion Battery with Life Extension Additive
Abstract
A system and/or method for replenishing lithium-ion battery
capacity that is lost due to side reactions over the lifetime of a
battery in one embodiment includes a battery with a first
electrode, a second electrode, a separator region configured to
electronically isolate the first and second electrodes, a first
portion of lithium metal encapsulated within a first ionically
insulating barrier configured to prevent transport of lithium ions
therethrough, a memory in which command instructions are stored,
and a processor configured to execute the command instructions to
(i) determine a first lithium content of the first electrode, (ii)
compare the first lithium content of the first electrode to a first
threshold, and (iii) activate the first portion of lithium metal
based on the comparison of the first lithium content to the first
threshold.
Inventors: |
Christensen; John F.;
(Mountain View, CA) ; Chaturvedi; Nalin;
(Sunnyvale, CA) ; Kozinsky; Boris; (Waban, MA)
; Albertus; Paul; (Mountain View, CA) ; Ahmed;
Jasim; (Mountain View, CA) ; Kojic; Aleksandar;
(Sunnyvale, CA) ; Lohmann; Timm; (Mountain View,
CA) ; Sanchez-Carrera; Roel S.; (Sommerville,
MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ROBERT BOSCH GMBH; |
Stuttgart |
|
DE |
|
|
Assignee: |
ROBERT BOSCH GMBH
Stuttgart
DE
|
Family ID: |
47221579 |
Appl. No.: |
13/667622 |
Filed: |
November 2, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61555357 |
Nov 3, 2011 |
|
|
|
Current U.S.
Class: |
429/50 ; 429/61;
429/62 |
Current CPC
Class: |
H01M 4/02 20130101; H01M
2/00 20130101; H01M 14/00 20130101; H01M 10/486 20130101; H01M
10/484 20130101; H01M 10/052 20130101; H01M 4/382 20130101; Y02T
10/70 20130101; Y02E 60/10 20130101 |
Class at
Publication: |
429/50 ; 429/61;
429/62 |
International
Class: |
H01M 2/00 20060101
H01M002/00; H01M 10/50 20060101 H01M010/50 |
Claims
1. A battery management system, comprising: a battery including: a
first electrode; a second electrode; a separator region configured
to electronically isolate the first and second electrodes; a first
portion of lithium metal encapsulated within a first ionically
insulating barrier configured to prevent transport of lithium ions
therethrough; a memory in which command instructions are stored;
and a processor configured to execute the command instructions to
(i) determine a first lithium content of the first electrode, (ii)
compare the first lithium content of the first electrode to a first
threshold, and (iii) activate the first portion of lithium metal
based on the comparison of the first lithium content to the first
threshold.
2. The battery management system of claim 1, wherein the processor
is further configured to execute the command instructions to (i)
determine a second lithium content of the second electrode, (ii)
compare the first lithium content of the first electrode and the
second lithium content of the second electrode, and (iii) activate
the first portion of lithium metal based on the comparison of the
first lithium content and the second lithium content.
3. The battery management system of claim 2, wherein the processor
is further configured to execute the command instructions to
activate the first portion of lithium metal when the first lithium
content of the first electrode plus the first portion of lithium
metal is also equal to the second lithium content.
4. The battery management system of claim 1, wherein: the battery
further includes a second portion of lithium metal encapsulated
within a second ionically insulating barrier configured to prevent
transport of lithium ions therethrough; and the processor is
further configured to executed the command instructions to activate
the second portion of lithium metal based on the comparison of the
first lithium content to the first threshold.
5. The battery management system of claim 4, wherein the processor
is further configured to execute the command instructions to (i)
determine a second lithium content of the second electrode, (ii)
compare the first lithium content of the first electrode and the
second lithium content of the second electrode, and (iii) activate
the second portion of lithium metal based on the comparison of the
first lithium content and the second lithium content.
6. The battery management system of claim 1, wherein: the battery
further includes a second portion of lithium metal encapsulated
within a second ionically insulating barrier configured to prevent
transport of lithium ions therethrough; and the processor is
further configured to executed the command instructions to (i)
compare the first lithium content to a second threshold and (ii)
activate the second portion of lithium metal based on the
comparison of the first lithium content to the second
threshold.
7. The battery management system of claim 1, wherein: the battery
further includes a second portion of lithium metal encapsulated
within a second ionically insulating barrier configured to prevent
transport of lithium ions therethrough; and the processor is
further configured to execute the command instructions to (i)
determine a second lithium content of the second electrode, (ii)
compare the second lithium content of the second electrode to a
second threshold, and (iii) activate the second portion of lithium
metal based on the comparison of the second lithium content to the
second threshold.
8. The battery management system of claim 7, wherein the processor
is further configured to execute the command instructions to (i)
compare the first lithium content of the first electrode and the
second lithium content of the second electrode, and (ii) activate
at least one of the first portion of lithium metal and the second
portion of lithium metal based on the comparison of the first
lithium content and the second lithium content.
9. The battery management system of claim 8, wherein the processor
is further configured to execute the command instructions to
activate the first portion of lithium metal and the second portion
of lithium metal when the first lithium content of the first
electrode plus the first portion of lithium metal plus the second
portion of lithium metal is also equal to the second lithium
content.
10. The battery management system of claim 8, wherein the processor
is further configured to execute the command instructions to
activate the first portion of lithium metal and the second portion
of lithium metal when the first lithium content of the first
electrode plus the first portion of lithium metal is also equal to
the second lithium content of the second electrode plus the second
portion of lithium metal.
11. The battery management system of claim 1, wherein the processor
is further configured to execute the command instructions to
control a compromise control control device to activate the first
portion of lithium metal by one or more of (i) applying a first
breach pressure to the first portion of lithium metal to fracture
the first barrier, (ii) increasing a temperature of the battery to
a first breach temperature to fracture the first barrier, and (iii)
changing a potential of the first electrode to a first barrier
potential.
12. The battery management system of claim 1, further comprising: a
compromise condition detector suite operably connected to the
processor and configured to detect one or more of (i) pressure
within the first electrode, (ii) temperature within the first
electrode, and (iii) potential of the first electrode.
13. A method for restoring lost capacity in a battery, comprising:
determining a first lithium content of a first electrode of the
battery; comparing the first lithium content of the first electrode
to a first threshold; and activating a first portion of lithium
metal based on the comparison of the first lithium content to the
first threshold, the first portion of lithium metal encapsulated
within a first ionically insulating barrier configured to prevent
transport of lithium ions therethrough.
14. The method of claim 13, further comprising: determining a
second lithium content of a second electrode of the battery;
comparing the first lithium content of the first electrode and the
second lithium content of the second electrode; and activating the
first portion of lithium metal based on the comparison of the first
lithium content and the second lithium content.
15. The method of claim 14, wherein the first portion of lithium
metal is activated when the first lithium content of the first
electrode plus the first portion of lithium metal is also equal to
the second lithium content.
16. The method of claim 13, further comprising: activating a second
portion of lithium metal based on the comparison of the first
lithium content to the first threshold, the second portion of
lithium metal encapsulated within a second ionically insulating
barrier configured to prevent transport of lithium ions
therethrough.
17. The method of claim 13, further comprising: comparing the first
lithium content to a second threshold; and activating a second
portion of lithium metal based on the comparison of the first
lithium content to the second threshold, the second portion of
lithium metal encapsulated within a second ionically insulating
barrier configured to prevent transport of lithium ions
therethrough.
18. The method of claim 13, further comprising: determining a
second lithium content of a second electrode of the battery;
comparing the second lithium content of the second electrode to a
second threshold; and activating a second portion of lithium metal
based on the comparison of the second lithium content to the second
threshold, the second portion of lithium metal encapsulated within
a second ionically insulating barrier configured to prevent
transport of lithium ions therethrough.
19. The method of claim 18, further comprising: comparing the first
lithium content of the first electrode and the second lithium
content of the second electrode; and activating at least one of the
first portion of lithium metal and the second portion of lithium
metal based on the comparison of the first lithium content and the
second lithium content.
20. The method of claim 13, wherein a compromise control device is
configured to activate the first portion of lithium metal by one or
more of (i) applying a first breach pressure to the first portion
of lithium metal to fracture the first barrier, (ii) increasing a
temperature of the battery to a first breach temperature to
fracture the first barrier, and (iii) changing a potential of the
first electrode to a first barrier potential.
21. The method of claim 1, wherein a compromise condition detector
suite is configured to detect one or more of (i) pressure within
the first electrode, (ii) temperature within the first electrode,
and (iii) potential of the first electrode.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/555,357, filed Nov. 3, 2012.
FIELD OF THE INVENTION
[0002] The present disclosure relates to batteries and more
particularly to lithium-ion batteries.
BACKGROUND
[0003] Rechargeable lithium-ion batteries are attractive energy
storage systems for portable electronics and hybrid-electric
vehicles because of their high energy density and rate capability.
However, they generally suffer degradation mechanisms that limit
their useful life. These degradation mechanisms can be classified
as power fade (an increase in internal resistance of the battery)
and capacity fade (a decrease in useable capacity). Capacity fade,
in turn, can be divided into (i) degradation or loss of the active
material that serves as a host to the lithium ions in the two
working electrodes and (ii) loss of charge due to side reactions at
one or both of the electrodes. Christensen, J. and J. Newman,
"Effect of Anode Film Resistance on the Charge/Discharge Capacity
of a Lithium-ion Battery", Journal of the Electrochemical Society,
150 (2003) A1416; Christensen, J. and J. Newman, "Cyclable Lithium
and Capacity Loss in Li-Ion Cells", Journal of the Electrochemical
Society, 152 (2005) A818.
[0004] A typical Li-ion cell 10, as shown in FIG. 1, contains a
negative electrode 20, a positive electrode 22, and a separator
region 24 between the negative and positive electrodes 20/22. Both
electrodes 20/22 contain active materials 26 and 28, respectively,
into which lithium can be inserted, inert materials 36, and a
current collector 38/40, respectively. The active materials 26/28
are also referred to as lithium-insertion materials. The separator
24 contains an electrolyte with a lithium cation, and serves as a
physical barrier between the electrodes 20/22 such that the
electrodes 20/22 are not electronically connected within the cell
10.
[0005] Typically, during charging, there is generation of electrons
at the positive electrode 22 and consumption of an equal amount of
electrons at the negative electrode 20, and these electrons are
transferred via an external circuit 30. In the ideal operation of
the cell 10, these electrons are generated at the positive
electrode 22 because there is extraction of lithium ions from the
active material 28 of the positive electrode 22, and the electrons
are consumed at the negative electrode 20 because there is
insertion of lithium ions into the active material 26 of the
negative electrode 20. During discharging, the exact opposite
reactions occur.
[0006] The main charge-transfer reactions that occur at the two
electrodes 20/22 during charge, which results in Li .sup.+ moving
in the direction of arrow 32, are:
LiP.fwdarw.Li++e-+P (at the positive electrode 22) and
Li++e-+N.fwdarw.LiN (at the negative electrode 20)
wherein P represents the positive electrode material 28 and N the
negative electrode material 26. Accordingly, LiP and LiN are the
positive electrode materials and negative electrode materials,
respectively, intercalated with lithium. For discharging, these
reactions proceed in the opposite direction with Li.sup.+ moving in
the direction of arrow 34.
[0007] The charge/discharge cycle for an ideal cell is represented
in FIGS. 2A-2E. As shown in the figures, lithium (represented by
shading) starts in the positive electrode in the discharged state
of the cell (FIG. 2A). During charge (FIG. 2B), lithium is
transferred to the negative electrode. At full charge, all of the
lithium is transferred to the negative electrode (FIG. 2C). During
the subsequent discharge (FIG. 2D), the opposite reactions occur,
and all of the lithium is transferred back to the positive
electrode at full discharge (FIG. 2E). In the ideal operation of
the cell, there are no other charge-transfer reactions, besides the
main reactions.
[0008] Side reactions have been defined as those charge-transfer
reactions that occur other than the insertion or extraction of
lithium ions into or out of the active material, with common
examples including decomposition of the solvent or formation of the
solid electrolyte interphase (SEI) at the negative electrode as
reported by Arora, P., R. E. White, and M Doyle, "Capacity Fade
Mechanisms and Side Reactions in Lithium-ion Batteries", Journal of
the Electrochemical Society, 145 (1998) 3647, and Aurbach, D., "The
Role of Surface Films on Electrodes in Li-ion Batteries", in
Advances in Lithium-Ion Batteries, W. A. van Schalkwijk and B.
Scrosati, Eds. Academic/Plenem Publishers: New York, 2002; p 7. For
non-ideal cells, some charge can be consumed via a side reaction.
This results in a permanent capacity loss if the side reaction is
not fully reversible. In contrast, the main reactions as described
above with respect to FIGS. 2A-2E are typically fully
reversible.
[0009] FIGS. 3A-3E depict an example in which an irreversible side
reaction occurs at the negative electrode 20 during charge,
consuming electrons that ideally should be consumed by the main
reaction. FIG. 3A represents the initial discharged state of the
cell. FIG. 3B represents the cell during charge and FIG. 3C
represents the cell after the cell is fully charged. FIG. 3D
represents the cell during discharge and FIG. 3E represents the
cell after the cell is fully discharged. In FIG. 3B, "S" is a
generic reactant that could represent the solvent, an anion, or a
contaminant. The product 5.sup.- may be soluble in the electrolyte,
or can form a solid precipitate with the lithium cation. Because
this reaction is irreversible in this example, the reverse reaction
does not occur during discharge (FIG. 3D), and the charge cannot be
transferred back to the positive electrode 22.
[0010] The small box 40 below the negative-electrode box 20 thus
represents charge that is consumed via the side reaction. It is
shaded after the cell is charged to show that some of the charge
has been consumed irreversibly (FIG. 3C). However, the total area
of the shaded regions in all of the boxes remains constant because
charge is conserved. While the example depicted in FIGS. 3A-3E
present a completely irreversible reaction, some side reactions may
be somewhat reversible, in which case a fraction of the charge
consumed by the side reaction can be returned to the positive
electrode.
[0011] The capacity of the cell is proportional to the number of
electrons that are reversibly transferred from one electrode to the
other via the external circuit. Thus, as seen from the example in
FIGS. 3A-3E, the cell's capacity is reduced because of side
reactions.
[0012] Some effort has been made to ameliorate the reduced capacity
which results from undesired side reactions. U.S. Pat. No.
6,025,093 issued to Herr in 1998, discloses a system wherein cells
have been designed to compensate for first-cycle lithium loss
during SEI formation. As noted above, SEI is a side reaction.
[0013] U.S. Pat. No. 6,335,115, issued to Meissner in 2002
describes the use of an auxiliary lithium electrode that
compensates for lithium loss throughout the life of the cell. In
the '115 patent, two means of isolating the auxiliary electrode
from the working electrodes are disclosed. One such isolation means
is ionic isolation and the second isolation means is an electronic
isolation. Ionic isolation involves an orientation of the battery
in which the lithium-ion containing electrolyte contacts the two
working electrodes, but not the auxiliary electrode. The lithium
auxiliary electrode is presumably always in electronic contact with
one of the working electrodes, but replenishment of lithium to the
depleted working electrode does not occur until the cell is
reoriented such that the electrolyte is in contact with both the
working electrode and the auxiliary electrode.
[0014] The ionic isolation approach has some limitations. For
example, in a lithium-ion battery the battery would have to be
designed such that the electrolyte does not completely fill the
pores of the separator and working electrodes. However, the porous
separator would naturally act as a wick that transports the
electrolyte to the region of the separator that contacts the
auxiliary electrode. Even residual electrolyte on the pores of this
region of the separator would allow transport of lithium from the
auxiliary electrode to the working electrode. Lithium transfer
would continue until the potentials of the working and auxiliary
electrodes equilibrated. Excessive lithium transfer, beyond the
point of capacity balance between the two working electrodes, would
result in reduction of the cell's capacity as reported by
Christensen, J. and J. Newman, "Effect of Anode Film Resistance on
the Charge/Discharge Capacity of a Lithium-ion Battery", Journal of
the Electrochemical Society, 150 (2003) A1416, and Christensen, J.
and J. Newman, "Cyclable Lithium and Capacity Loss in Li-Ion
Cells", Journal of the Electrochemical Society, 152 (2005)
A818.
[0015] Moreover, shorting of the
auxiliary-electrode-working-electrode circuit via imperfect ionic
isolation would lead to rapid transfer of lithium to the working
electrode and possible deposition of lithium on the electrode
surface. Such lithium deposition can pose a safety risk and/or
degrade the cell because the lithium metal reacts rapidly and
exothermically with the organic solvent used in the electrolyte as
reported by Arora, P., M. Doyle, and R. E. White, "Mathematical
Modeling of the Lithium Deposition Overcharge Reaction in
Lithium-ion Batteries Using Carbon-based Negative Electrodes",
Journal of the Electrochemical Society, 146 (1999) 3543.
[0016] Even if it were possible to maintain ionic isolation of the
auxiliary electrode until lithium transfer is required, the cell
design disclosed in the '115 patent would require additional
electrode and separator material that is unutilized. Moreover, the
orientation of the cell in FIG. 1 of the '115 patent is such that
the two working electrodes are not in ionic contact, and therefore,
lithium transport between the two electrodes is impossible in this
orientation.
[0017] Even if the foregoing shortcomings are addressed, a system
which relies upon reorientation of the battery significantly
reduces the number of potential applications. For example,
battery-powered devices such as power tools may be used in any
orientation, meaning that the auxiliary-electrode-working-electrode
circuit could be closed unintentionally during standard operation
of the battery. Hence, the device disclosed in the '115 patent
appears to be limited to applications that have a fixed
orientation.
[0018] Another approach disclosed in U.S. Pat. No. 7,726,975,
issued to Christensen et al. in June 2010, involves the use of an
auxiliary lithium electrode that can be electronically connected to
or isolated from one or more of the working electrodes. The system
in the '975 patent circumvents the issues raised above by relying
upon electronic, rather than ionic, isolation of the lithium
reservoir electrode (LRE) from the working electrodes. The '115
patent also discloses such electronic isolation. However, the
lithium auxiliary electrode proposed in the '115 patent is placed
"between the positive and negative electrodes." Such placement
would reduce the uniformity of current distribution, and therefore
the rate capability of the cell, when transferring lithium from one
working electrode to the other. The approach in the '975 patent
avoids this problem by placing the LRE outside the current path
between the two working electrodes.
[0019] Approaches that rely upon an auxiliary lithium electrode
typically suffer from the problem of large length scales associated
with the distance of the auxiliary electrode from the working
electrodes. A typical length scale between two working electrodes,
which are pressed together on either side of a porous separator, is
on the order of 100 microns, while the distance from an auxiliary
lithium electrode to the farthest region of each working electrode
can be on the order of 1 cm or more, even when the auxiliary
lithium electrode is sandwiched between the two working electrodes.
This is because the auxiliary electrode may not span the entire
separator, as this would block ionic transport from one working
electrode to the other. Moreover, dendrites could easily form and
short one or more working electrode with the auxiliary electrode in
this case.
SUMMARY
[0020] A battery management system in one embodiment includes a
battery including a first electrode and a second electrode, a
separator region configured to electronically isolate the first and
second electrodes, and a first portion of lithium metal
encapsulated within a first ionically insulating barrier configured
to prevent transport of lithium ions therethrough. The battery
management system further includes a memory in which command
instructions are stored and a processor configured to execute the
command instructions to (i) determine a first lithium content of
the first electrode, (ii) compare the first lithium content of the
first electrode to a first threshold, and (iii) activate the first
portion of lithium metal based on the comparison of the first
lithium content to the first threshold.
[0021] The battery management system implements a method to restore
the lost capacity in the battery. The method includes determining a
first lithium content of a first electrode of the battery,
comparing the first lithium content of the first electrode to a
first threshold, and activating transfer of a first portion of
lithium metal to the electrode based on the comparison of the first
lithium content to the first threshold, the first portion of
lithium metal encapsulated within a first ionically insulating
barrier configured to prevent transport of lithium ions
therethrough until the BMS activates the transfer (i.e., causes the
barrier to become transparent to Li ions).
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 depicts a typical prior art Li-ion battery;
[0023] FIGS. 2A-2E depict an ideal charge/discharge cycle of the
battery of FIG. 1;
[0024] FIGS. 3A-3E depict a charge/discharge cycle of the battery
of FIG. 1 with a side reaction;
[0025] FIG. 4 depicts a Li-ion battery incorporating a selectively
activated additive in accordance with the disclosure;
[0026] FIG. 5 depicts a cross sectional view of an additive of FIG.
4;
[0027] FIG. 6 depicts a battery management system that can be used
to control selective activation of the additive of FIG. 5;
[0028] FIGS. 7A-7C depict the effect of the additive of FIG. 4 on
the lithium content in the battery of FIG. 4; and
[0029] FIG. 8 depicts a procedure that can be executed under the
control of the battery management system of FIG. 6 to selectively
activate a lithium additive.
DESCRIPTION
[0030] For the purpose of promoting an understanding of the
principles of the disclosure, reference will now be made to the
embodiments illustrated in the drawings and described in the
following written specification. It is understood that no
limitation to the scope of the disclosure is thereby intended. It
is further understood that the disclosure includes any alterations
and modifications to the illustrated embodiments and includes
further applications of the principles of the disclosure as would
normally occur to one skilled in the art to which this disclosure
pertains.
[0031] FIG. 4 shows a cell with Li replenishment additives
contained in the positive electrode. The cell 100 contains a
negative electrode 102 and a positive electrode 104. The negative
electrode 102 includes a lithium insertion material 106, inert
materials 108, and a current collector 110. The positive electrode
104 includes a lithium insertion material 116, inert materials 108,
and a current collector 120. The cell 100 also includes a separator
region 122 that contains an electrolyte with a lithium cation, and
serves as a physical barrier between the electrodes 102/104 such
that the electrodes 102/104 are electronically isolated within the
cell 100. The electrolyte enables lithium-ion transfer between the
negative and positive electrodes 102/104, which are referred to
herein as the working electrodes.
[0032] With reference to FIGS. 4 and 5, the cell 100 additionally
contains additive 130 which is provided in either or both of the
electrodes 102/104 in different embodiments. The additive 130
consists of Li metal particles 132 that are coated with a material
134 that is ionically insulating and, in some embodiments, is
electronically conductive. Ionic insulation or barrier 134 prevents
transport of Li from the particles 132 to the surrounding composite
electrode during normal cell operation. In the embodiment of FIG.
4, a second additive 140 is provided. The additive 140 consists of
Li metal particles 142 that are coated with a material 144 that is
ionically insulating and, in some embodiments, is electronically
conductive.
[0033] The two batches of additives 130/140 are independently
activated by compromising the insulating material 134/144, such as
by breaking, dissolving, or decomposing the insulating material
134/144, or by causing the insulating material 134/144 to be
ionically conductive and therefore permeable to Li ions. The
activation step in some embodiments involves increasing the
temperature of the cell 100 outside the normal operating range,
compressing the cell 100 such that enough stress is imparted to the
barrier 134 that it fractures, injecting an additive into the
electrolyte of the cell 100 that reacts with and decomposes the
barrier 134, or changing the potential of the electrode that
contains the additive 130 beyond its normal operating range. The
insulating material 144 can be independently compromised either by
providing an insulating material 144 with a different compromising
mechanism, or with a different set point. Thus, at a first
temperature the insulating material 134 fractures, while the
insulating material 144 does not fracture until a second, higher
temperature or cell compression is achieved.
[0034] The insulating material 134/144 is preferably at least
partially electronically conductive to facilitate transport of
electrons from the Li metal core 132/142 to the electronically
conductive matrix of the positive electrode 104. Hence, when
activated, electrons spontaneously are transferred from the Li
metal 132 to the electrode active material 116 through
electronically conductive phases, while Li ions are spontaneously
transferred to the active material 116 through ionically conductive
phases. The transfer is spontaneous because the active insertion
materials 116 have a potential higher than that of Li metal 132.
While only two insulating materials 134/144 are identified above,
several different coatings may be applied to various additives in a
particular embodiment. Alternatively, the thickness of the shells
may be controlled to provide different compromise set points.
[0035] Beneficially, the cell 100 in one embodiment is manufactured
in any desired configuration (e.g., spirally wound, prismatically
stacked, etc.), and has two terminals, one each for the positive
electrode 104 and negative electrode 102.
[0036] In one embodiment, the cell 100 is incorporated into a
battery management system 200 which is depicted in FIG. 6. The
battery system 200 includes an I/O device 202, a processing circuit
204 and a memory 206. The I/O device 202 in one embodiment includes
a user interface, graphical user interface, keyboards, pointing
devices, remote and/or local communication links, displays, and
other devices that allow externally generated information to be
provided to the battery system 200, and that allow internal
information of the battery system 200 to be communicated
externally. The battery management system 200 in one embodiment is
configured to obtain measurements directly from the cell 100 or to
obtain data from an intermediate source.
[0037] The processing circuit 204 in some embodiments is suitably a
general purpose computer processing circuit such as a
microprocessor and its associated circuitry. The processing circuit
204 is operable to carry out the operations attributed to it
herein.
[0038] Within the memory 206 are various program instructions 208.
The program instructions 208, some of which are described more
fully below, are executable by the processing circuit 204 and/or
any other components as appropriate. Insulating material databases
210 are also located within the memory 206. The insulating material
databases 210 stores data used to identify the conditions required
for compromising the insulating material 134/144 such as a
pressure, temperature, additive, etc.
[0039] The battery management system 200 further includes
compromise control equipment 212 and compromise condition detector
suite 214. The compromise control equipment 212 is configured to
establish and maintain conditions which result in compromising the
insulating material 134/144.
[0040] During normal operation, the positive and negative electrode
terminals 104/102 are connected to either end of a load 150 during
discharge, and to a power supply 150 during charge (FIG. 4). The
additives 130/140 remain inactive during normal operation. When the
battery system 200 determines it is appropriate to replenish the
capacity of the cell 100 lost due to side reactions, the additive,
or a single batch of additives 130/140, is activated by
establishing conditions which compromise the insulating material
134/144 using the compromise control equipment 212. In one
embodiment, the compromise control equipment 212 is equipment used
during normal operation of the battery such as a heating element.
In another embodiment, the compromise control equipment 212 is used
uniquely for establishing compromise conditions, such as a pressure
applying device, a heating element, or syringe for adding chemicals
to the electrolyte.
[0041] Accordingly, a compromising condition is established which
in various embodiments includes one or more of increasing the
temperature of the cell 100 outside the normal operating range,
compressing the cell 100 such that enough stress is imparted to the
additives 130/140 that it fractures, injecting an additive into the
electrolyte of the cell 100 that reacts with and decomposes the
barrier(s) 134/144, or changing the potential of the electrode that
contains the additives 130/140 beyond its normal operating range.
In one embodiment, the BMS 200 uses the compromise condition
detector suite 214 to monitor the precise environment established
by the compromise control equipment 212.
[0042] Once the additives 130/140 are activated, lithium ions are
transferred ionically from the Li metal core(s) 132/142 of the
additives 130/140 into the active insertion material 116 that is a
constituent of the composite electrode that contains the additive.
This transfer in one embodiment is facilitated by simultaneous
transport of electrons through the electronically conductive
additives 130/140, or electronically conductive portion of the
additives 130/140, or by compression of the electrode to establish
electronic contact directly between the active insertion material
116 and the Li metal core(s) 132/142 of the additives 130/140.
Hence, the cell capacity can be restored to its original value, or
close to its original value.
[0043] FIGS. 7A-7C illustrate how charge from the additive
batch(es), which is contained in the positive electrode, replaces
the charge that was lost due to the side reaction illustrated in
FIGS. 3A-E. To replace the lost charge of a cell in the discharged
state due to the side reaction 40 (FIG. 7A), the additive batch 130
or batches are activated in the positive electrode 104, allowing
electrons to flow from the additive 130 to the positive electrode
active material in the direction of arrow 52 (FIG. 7B).
Simultaneously, lithium dissolves from the additive 130 and is
transferred through the electrolyte in the positive electrode 104
to the active material 116, where it is inserted via the main
insertion reaction (FIG. 7B). The correct amount of charge to be
transferred is determined by the battery management system 200,
such that the cell returns to its original capacity, or close to
its original capacity (FIG. 7C). This process in one embodiment is
repeated several times throughout the life of the cell, depending
upon the number of batches of additive available for independent
activation.
[0044] An inherent challenge in using such an additive is that it
is difficult to determine the amount of Li to be transferred to
each of the working electrodes. Insertion of too much lithium into
the working electrodes can degrade the cell and create a
significant safety risk. For example, excess lithiation of one or
more working electrode could result in a capacity imbalance between
the two electrodes, thereby reducing the capacity of the cell below
the value of an optimally balanced cell. Therefore, it is important
to know the appropriate time to activate the additive, or additive
batch, such that the active insertion material is not
overlithiated
[0045] The present system accounts for this important need to
determine the amount of lithium to be transferred by using a
battery management system (BMS) 200 for determining the amount of
capacity that has been lost from the system due to side reactions.
The BMS 200 must therefore estimate the state of charge (SOC) of
each working electrode. The SOC of each working electrode
corresponds to the amount of lithium contained in it. When the
lithium concentration is at its maximum value, the SOC of the
electrode is 1, and when it is at its minimum, the SOC is 0. The
additive is used to increase the SOC of one or both of the working
electrodes through the selective transfer of lithium ions and
electrons.
[0046] With reference to FIG. 8, the processor 204 executes command
instructions 208 stored within memory 206 in accordance with a
procedure 300 to determine the lost cell capacity and selectively
activate the additive 130/140 if certain conditions are met.
Initially, criteria for operating the system 200 are stored in the
memory 206, at block 302. The criteria may be stored in the form of
a battery model and a diagnostic algorithm with different additive
activation profiles provided for different factors.
[0047] In some embodiments, multiple algorithms are associated with
the cell depending on the desired complexity of the system. By way
of example, the criteria in some of these embodiments include,
among other criteria, a nominal charge voltage ("V.sub.c") and a
nominal discharge voltage ("V.sub.d") for the cell. Additionally,
in some of these embodiments, an initial open cell potential
("OCP")/SOC relationship for the cell is stored in the memory. The
stored criteria provide values for the algorithm that the processor
uses to implement the different additive activation profiles. The
criteria stored in the memory are obtained in any desired
manner.
[0048] The BMS 200 uses the battery model and the diagnostic
algorithm to deconvolute the SOCs of the two working electrodes
from measurements of the full-cell potential and current (block
304). An example of a system and method that can be modified to
calculate the SOC of the working electrodes is found in U.S.
application Ser. No. 12/396,918, filed on Mar. 3, 2009, the entire
contents of which are incorporated by reference herein. The
estimated SOC values are then transformed into a total lithium
content in each electrode by the BMS 200 (block 306).
[0049] The BMS 200 computes the difference between the present Li
content in each electrode and the desired Li content in each
electrode that indicates a balance of capacity between the two
electrodes (block 308). The BMS 200 compares this difference to the
amount of Li contained in one or more additive batches in the
respective electrode(s) using data stored in the memory 206 (block
310). If the amount of Li contained in the batches is more than the
difference between the present and desired Li content in the
electrode(s) at block 312, the process 300 returns to block 304 for
continued monitoring of the SOCs of the electrode(s). If the amount
of Li contained in one of the batches is close to, for example,
within 2% or less of the difference between the present and desired
Li content in the electrode(s) at block 312, the process 300
continues to block 314. At block 314, the BMS activates the one or
more batches of additive to bring the Li content of the electrodes
to the desired level.
[0050] In one embodiment, the BMS 200 is located in a single
device. In another embodiment, portions of the BMS 200 are located
apart from other portions of the BMS 200. In yet other embodiments,
functions of the processor are performed by multiple processors. By
way of example, the electrodes and Li additives in one embodiment
are located within a vehicle battery . A processor carried in the
vehicle monitors the SOC of the battery and provides a warning
signal to a user when the available Li content of one or more of
the electrodes falls below a predetermined threshold. The user then
proceeds to a service station where the compromise control
equipment is located and used to activate additional Li under
control of a processor associated with the compromise control
equipment. In some embodiments, communications between the
processor within the vehicle and the processor within the
compromise control equipment are established using a CAN
communication bus or other communication protocol/system.
[0051] While the disclosure has been illustrated and described in
detail in the drawings and foregoing description, the same should
be considered as illustrative and not restrictive in character. It
is understood that only the preferred embodiments have been
presented and that all changes, modifications and further
applications that come within the spirit of the disclosure are
desired to be protected.
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